System for generating an analogue i/q signal from two or more data streams

ABSTRACT

The invention relates to a method for generating an I/Q signal for an I/Q modulator ( 10 ). Said signal is composed of two or more data streams, which have been edited according to identical or different digital modulation methods. In said method, a known modulation encoder is used to generate corresponding digital I/Q values from a first inputted digital data stream. Said I/Q values then undergo a digital-analogue conversion ( 8 ) that generates the corresponding analogue I/Q signals. The invention is characterised by an additional modulation generator that calculates digital I/Q values, or generates I/Q values from an additional inputted digital data stream. The digital I/Q values of the modulation encoder and the digital I/Q values of the modulation generator ( 10 ) are then added together, using digital adders (A 3 ) located upstream of the digital-analogue converter ( 8 ).

[0001] The invention relates to an arrangement for generating an analogor digital I/Q signal for an I/Q modulator, which signal is composed oftwo or more data streams processed by identical or different digitalmodulation methods.

[0002] In modern transmission engineering, I/Q signals are used for datatransmission that are modulated onto a high-frequency carrier in an I/Qmodulator. There are extremely diverse modulation standards for the I/Qmodulator for generating said I/Q signals. A frequently used modulationmethod is, for example, the time-division multiplex access method TDMAused in Europe and the USA for mobile-radio purposes or the codedivision multiplex method CDMA. In such systems, it is often desirableto transmit, via one and the same high-frequency carrier and using thesame I/Q modulator, two or more I/Q signals that have been processedaccording to the same digital modulation standard, but with differentinput data streams, or that have been processed according to differentdigital modulation standards. Said different I/Q signals can each begenerated separately in respective modulation encoders or modulationgenerators and then added; however, this is relatively expensive.

[0003] The object of the invention is therefore to provide anarrangement with which this is possible with substantially reducedcircuit expenditure.

[0004] Proceeding from an arrangement according to the preamble of themain claim, this object is achieved by the characterizing features ofthe latter. Advantageous developments emerge from the subclaims.

[0005] In accordance with the invention, the two or more data streamsprocessed by identical or different digital modulation methods arealready combined upstream of the D/A conversion in a purely digital wayand, specifically, in a standard modulation encoder such as is known perse for processing a digital data stream to form an analog I/Q signal. Itis only necessary to insert, at predetermined points in the I/Qbranches, suitable adding stages via which the digital I/Q values of afurther modulation generator can then already be added upstream of theD/A conversion. In this way, a number of assemblies become superfluousfor the signal processing of the I/Q values of the additional modulationgenerator since said assemblies, for example the clock generator, thedigital signal processor for the control, the D/A converter and thedownstream low-pass filter, can be used concomitantly by the modulationencoder. In this connection, the additional modulation generator can beof any known type. It may be, for example, a further modulation encoderthat generates the I/Q values to be added from an internal or externaldigital input data stream by encoding and mapping according to any knownmodulation standard. For measurement purposes, said additionalmodulation generator may also contain, in a memory, pre-calculated I/Qvalues that are read out in the system clock and are fed to adders, suchas is known per se, for example, in the case of the AMIQ modulationgenerator supplied by Rohde & Schwarz.

[0006] The method according to the invention is particularly well suitedfor an arrangement for generating a digitally modulated test signalaccording to the earlier, non-predisclosed patent application DE 199 57093 A1 of Rohde & Schwarz, in which some of the transmission channels ofthe test signal are generated in a modulation encoder directly from aninternal or external modulation data stream according to a predeterminedmodulation standard and in which the I and Q values for at least some ofthe remaining channels of the test signal are fed from a memory to themodulation encoder as a pre-calculated modulation data sequence oflimited length; the I and Q values generated separately in this way arethen added and fed to the I/Q modulator. The disclosure in PatentApplication DE 199 57 093 A1 is incorporated in its full scope in thepresent patent application.

[0007] The invention is explained in greater detail below by referenceto a diagrammatic drawing using an exemplary embodiment.

[0008] The figure shows the basic circuit diagram of a known modulationencoder 11, such as is used, for example, in the SMIQ vector signalgenerator supplied by Rohde & Schwarz, data sheet PD757.4582. Saidmodulation encoder 11 comprises an encoder and mapping unit 1, 2 inwhich corresponding I and Q values are generated from the data stream ofan internal or external data source 3 depending on the chosen type ofmodulation. From the mapping unit 2, the I/Q values reach a base-bandfilter 4 in which a suitable pulse shaping is performed, and then amodulation format converter 5 in which the input signals are convertedeither into a linear PSK or QAM modulation or into a nonlinear FSKmodulation. Provided downstream of said modulation format converter isan interpolation filter 6. The sequence of the stages 5 and 6 can alsobe interchanged. A correction filter 7 may furthermore be optionallydisposed downstream of the interpolation filter 6. The I/Q valuesprocessed digitally in this way in separate I and Q branches aretransformed into corresponding analog I/Q signals in the D/A converter 8and, after traversing low-pass filters 9, are then fed to the actual I/Qmodulator 10, in which said signals are modulated onto a high-frequencycarrier.

[0009] In addition to said known modulation encoder arrangement, addingstages A1 to A3 are also inserted in the digital I/Q branches and,specifically, adding stages A1 can be disposed between the mapping unit2 and the base-band filters 4, or adding stages A2 can be disposedbetween the modulation format converter 5 and the interpolation filter6, or adding stages A3 may first be added downstream of theinterpolation filter 6, but still upstream of the correction filter 7(if present) and the D/A converter 8.

[0010] In addition to said modulation encoder 11 supplemented by one ormore adding stages, a further modulation generator 12 is provided thatsupplies I/Q values again generated by a known complex type ofmodulation at its I/Q output 13. In the exemplary embodiment shown, saidadditional modulation generator 12 is designed as a so-called arbitrarywaveform generator, such as is used, for example, in the AMIQ appliancesupplied by Rohde & Schwarz, data sheet PD 757.3970.12. The calculated Iand Q values are stored in a memory 15. They can be read out of saidmemory 15 as I/Q values to the output 13 under the control of a clockgenerator and a corresponding address generator. The reading-in andreading-out of the data from the data source 3 into the encoder 1 andthe reading-out of the I/Q values from the memory 15 are synchronized bymeans of the synchronization unit 16. The I/Q values from the output 13can now be fed either to the adding stages A1, A2 or A3 so that thedigital I/Q values of the additional modulation generator 12 arecombined with the digital I/Q values of the modulation encoder 11 and,after digital/analog conversion, are then fed as composite signals tothe I/Q modulator 10 and are broadcast by one and the samehigh-frequency carrier.

[0011] If the I/Q values from output 13 are fed to the adders A1 (theadders A2 and A3 may be omitted or bypassed in this case), the I/Qvalues of the modulation encoder 11 from the output of the mapping unit2 are added in real time and in symbol timing to the I/Q values of themodulation generator 12, the base-band filters being adjusted in such away that, as in the case of modulation encoders, they normally bringabout a pulse shaping. In this type of combination via adder A1, thebase-band filters and the modulation format (linear PSK or QAM, or FSKmodulation) are identical for both I/Q values.

[0012] If the I/Q values are fed from the output 13 to the adders A2,the I/Q values are brought together upstream of the interpolationfilter. In order to obtain identical data rates in each case under thesecircumstances, the I/Q values in the modulation generator 12 are eitheralready suitably prepared during the data storage in the memory 15 or anadditional data rate converter that is not shown is inserted inaddition. In this case, the base-band filtering for the two I/Q valuesmay be different. Since the adding only takes place downstream of themodulation format converter, different modulation formats may also beused.

[0013] If the sequence is interchanged between the units 5 and 6 (themodulation format converter 5 is disposed downstream of theinterpolation filter 6), the addition takes place upstream of themodulation format conversion and, in this case, the modulation formatscannot be chosen differently for the two signals.

[0014] Finally, a third possibility is to only bring the signalstogether upstream of the D/A converter 8 or a correction filter 7possibly present via the adder A3.

[0015] In the same way, I/Q values of two or more additional modulationgenerators 12 may also be combined with the I/Q values of the modulationencoder 11 and this may take place at any of the points A1, A2 or A3,the adders being provided in this case with three or more inputs.However, the adding can also be partitioned over various points, forexample in such a way that the I/Q values of a first modulationgenerator 12 are added via the adders A1, the I/Q values of a secondmodulation generator 12′ are added via the adders A2, etc.

[0016] The arrangement can also be used for processing the I/Q values ofthe modulation generator 12, the encoder 1 and the mapping unit 2 notbeing operative in this case. Only the I/Q values of the modulationgenerator 12 are therefore fed to the base-band filter via the addingstages A1. The base-band filter 4 is in this case programmed as alow-pass filter for band limitation or as an interpolation filter, inwhich case the actual interpolation filter 6 can either be omitted oradjusted in such a way that it acts as a cascaded interpolation filter.All the errors that occur in the signal path can be corrected by aninserted correction filter 7.

1. Arrangement for generating an I/Q signal for an I/Q modulator (10)that is composed of two or more data streams processed by identical ordifferent digital modulation methods, characterized by the use of amodulation encoder (11) known per se comprising the series connection ofan encoding and mapping unit (1, 2), a downstream digital base-bandfilter (4) whose filter properties are adjustable, a downstream digitalmodulation format converter (5), an interpolation filter (6) disposedupstream or downstream of said modulation format converter (5),optionally, an additional digital correction filter (7) and adigital/analog converter (8) with downstream analog low-pass filter (9),wherein, in said modulation encoder (11), corresponding digital I/Qvalues are generated from a first digital input data stream (3) and thecorresponding analog I/Q signals are generated therefrom afterdigital/analog conversion, and also at least one further modulationgenerator (12) in which calculated digital I/Q values or digital I/Qvalues generated from a further digital input data stream are generated,wherein the digital I/Q values of the modulation encoder (11) and thedigital I/Q values of the modulation generator (12) are added via adders(A1, A2, A3) disposed upstream of the digital/analog converter (8). 2.Arrangement according to claim 1, characterized in that the adders (A1)are disposed in the I/Q branches of the modulation encoder (11) upstreamof the band-pass filter (4).
 3. Arrangement according to claim 1 for amodulation encoder, in which the modulation format converter (5) isdisposed downstream of the base-band filter (4) and upstream of theinterpolation filter (6), characterized in that the adders (A2) aredisposed between the modulation format converter (5) and theinterpolation filter (6).
 4. Arrangement according to claim 1 for amodulation encoder, in which the modulation format converter (5) isdisposed downstream of the interpolation filter (6), characterized inthat the adders (A2) are disposed between base-band filter (4) andinterpolation filter (6).
 5. Arrangement according to claim 1,characterized in that the adders (A3) are disposed in the I/Q branchesdownstream of the interpolation filter (6), but upstream of thedigital/analog converter (8) and upstream of any correction filter (7)present.